Communication method in mobile communication system, and mobile station and base station in the same system

ABSTRACT

The present method adds uplink data to a transmission request sent to the base station from the mobile station for obtaining permission for data transmission, or to a channel establishment request sent from the mobile station to the base station for establishing a channel in order to send the transmission request therethrough. This makes it possible to suppress delay caused by negotiation prior to actual uplink data transmission as much as possible, thereby realizing efficient uplink data transmission, that is, improved throughput of uplink communication.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to JapaneseApplication No. 2005-183223 filed on Jun. 23, 2005 in Japan, thecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a communication method in a mobilecommunication system and a mobile station and a base station in the samesystem. The invention relates particularly to a technique suitable toimprove the throughput of uplink data communication from the mobilestation to the base station.

(2) Description of Related Art

In the current 3GPP (3rd Generation Partnership Project),standardization of W-CDMA (Wideband-Code Division Multiple Access),which is one of the schemes of the third-generation mobile communicationsystem, is in progress. One of the themes of the standardization is theHSDPA-(High Speed Downlink Packet Access) scheme which provides agreat-capacity high-speed packet data transfer (about 14 Mbps atmaximum) in the downlink direction from a base station to a mobilestation. Further, the HSUPA (High Speed Uplink Packet Access) scheme,which can be regarded as HSDPA in the uplink direction from a mobilestation to a base station, is under investigation (see, for example, thefollowing non-patent document 1).

In such high-speed data transmission, data transmission scheduling forefficient sending-out of data packet is important. In HSUPA, schedulingis determined based on such information as reception quality, the amountof buffer remaining, priority, and so on. These information items arenotified from a mobile station to a base station as SchedulingInformation (SI) in form of an uplink transmission request prior touplink transmission.

-   [Non-patent Document 1] 3rd Generation Partnership Project (3GPP);    Technical Specification Group Radio Access Network; “TS 25.309    V6.2.0 (2005-03) FDD Enhanced Uplink Overall Description Stage 2    (Release 6)”

In the present 3GPP specification, communication execution by HSUPA isperformed after establishment of dedicated radio channels, and asprocedures from call generation to call setting and HSUPA application,known procedures applied. Accordingly, delay occurs between a datatransmission request on a terminal and actual data transmission.

For example, as shown in FIG. 25, a mobile station (UE: User Equipment)100 sends an access request to a base station (BTS: Base TransceiverStation) 200 (step S100) by a random access method. Upon receipt of areply to the access request from the base station 200 (step S200), themobile station 100 sends a dedicated radio channel establishment requestto the base station 200 (step S300). When a reply to the channelestablishment request is received by the mobile station 100 (step 400),the mobile station 100 sends a transmission rate request to the basestation 200 (step S500). When a rate is assigned by the base station 200(step S600) in response to the transmission rate request, the mobilestation 100 eventually starts data transmission (steps S700 and S900).Here, when the data transmitted is normally received by the base station200, ACK is sent back to the mobile station 100, and when the datatransmitted is not received normally, NACK is sent back to the mobilestation 100 (step S800). Upon receipt of NACK, the mobile station 100performs data retransmission.

Under a condition where the data rate is low, delay caused by suchnegotiation prior to actual uplink data transmission is inconspicuous,but as the data rate increases, the delay becomes a considerableproblem. In addition, for realization of “Always on” by radio, it ispreferable that connection delay be as small as possible.

SUMMARY OF THE INVENTION

With the foregoing problems in view, it is an object of the presentinvention to suppress delay caused by negotiation prior to actual uplinkdata transmission as much as possible, thereby realizing efficientuplink data transmission, that is, an improved throughput of uplinkcommunication.

In order to accomplish the above object, according to the presentinvention, the following communication method, mobile station, and basestation are provided.

(1) As a generic feature, there is provided a communication method in amobile communication system including at least one mobile station and abase station, which performs radio communication with the mobilestation, the communication method comprising: on the mobile station,adding uplink data to a transmission request sent to the base stationfor obtaining permission for data transmission, or to a channelestablishment request sent to the base station for establishing achannel in order to send the transmission request therethrough.

(2) As another generic feature, there is provided a communication methodin a mobile communication system including at least one mobile stationand a base station, which performs radio communication with the mobilestation, wherein the base station is operable in a first mode in whichthe base station's permission is not necessary when the mobile stationtransmits uplink data, and a second mode in which the base station'spermission is necessary when the mobile station transmits uplink data,the method comprising: on the base station, monitoring an uplinkcommunication state between the base station and the mobile station;operating in the first mode if the uplink communication state is of aspecific or higher level of quality; and operating in the second mode ifthe uplink communication state is of quality lower than the specificlevel.

(3) As yet another generic feature, there is provided a mobile stationfor a mobile communication system including at least one mobile stationand a base station, which performs radio communication with the mobilestation, the mobile station comprising: a transmitter means whichtransmits a transmission request to the base station for obtainingpermission for data transmission or a channel establishment request tothe base station for establishing a channel in order to send thetransmission request therethrough; and a data adding means which addsuplink data to the transmission request or to the channel establishmentrequest.

(4) As a further generic feature, there is provided a base station for amobile communication system including at least one mobile station and abase station, which performs radio communication with the mobilestation, the base station comprising: a reply information transmittermeans which transmits reply information, indicating whether or not theuplink data sent from the mobile station has been normally received, tothe mobile station; and a notification information adding means whichadds transmission permission/non-permission notification information,indicating whether or not data transmission is permitted in response tothe transmission request, to the reply information to be sent to themobile station.

(5) As a still further generic feature, there is provided a base stationfor a mobile communication system including at least one mobile stationand a base station, which performs radio communication with the mobilestation, wherein the mobile station is operable in a first mode in whichthe base station's permission is not necessary when the mobile stationtransmits uplink data, and a second mode in which the base station'spermission is necessary when the mobile station transmits uplink data,the base station comprising: an uplink communication state monitoringmeans which monitors an uplink communication state between the basestation and the mobile station; an evaluating means which evaluateswhether or not the communication state monitored by the communicationstate monitoring means is of a specific or higher level of quality; anda mode selecting means which selects the first mode as an operation modeif the evaluation result is positive, and which selects the second modeas an operation mode if the evaluation result is negative.

(6) As a preferred feature, the base station for a mobile communicationsystem, further comprises: a data collision monitoring means whichmonitors, while operating in the first mode, whether or not a collisionoccurs in uplink data transmission from two or more mobile stations; anda retransmission timing notifying means which notifies each of themobile stations, if an occurrence of a collision is detected by the datacollision monitoring means, of retransmission timing in the uplink datatransmission.

(7) As another generic feature, there is provided a mobile station for amobile communication system including at least one mobile station and abase station, which performs radio communication with the mobilestation, in which mobile communication system the base station notifies,if a collision occurs in uplink data transmission from two or moremobile stations, each of the mobile stations of retransmission timing inthe uplink data transmission, the mobile station comprising: a uplinkdata generating means which generates uplink data including: a useridentification portion identifying each mobile station; and a dataportion, which is a message body; an uplink data transmitter means whichtransmits the uplink data generated by the uplink data generating meansto the base station.

(8) As a preferred feature, the uplink data generating means generatesthe uplink data as data having a fixed data length.

(9) As another preferred feature, the uplink data generating meansincludes an encoding means which encodes the data portion based oninformation of the user identification portion.

(10) As yet another preferred feature, the uplink data generating meansincludes an inserting means which inserts information of the useridentification portion into the data portion.

The above-described invention realizes efficient data transmission.Delay at the time of call setting is expected to be reduced andimprovement in throughput is also expected.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a construction of a radio mobilestation, which is a constituent of a mobile communication systemaccording to a first embodiment of the present invention;

FIG. 2 is a block diagram showing a construction of a radio basestation, which is a constituent of the mobile communication systemaccording to the first embodiment of the present invention;

FIG. 3 is a sequence diagram for describing an operation (uplinkcommunication method) of a mobile communication system of the firstembodiment;

FIG. 4 is a diagram showing a frame construction of an uplinktransmission request according to the first embodiment;

FIG. 5 is a block diagram showing a construction of a radio mobilestation, which is a constituent of a mobile communication systemaccording to a second embodiment of the present invention;

FIG. 6 is a block diagram showing a construction of a radio basestation, which is a constituent of the mobile communication systemaccording to the second embodiment of the present invention;

FIG. 7 is a sequence diagram for describing an operation (uplinkcommunication method) of a mobile communication system of the secondembodiment;

FIG. 8 is a diagram showing a frame construction of a random accesssignal according to the second embodiment;

FIG. 9 is a sequence diagram for describing an operation (uplinkcommunication method) of a mobile communication system according to amodified example of the second embodiment;

FIG. 10 is a diagram showing a frame construction of a downlink signalaccording to the second embodiment;

FIG. 11 is a flowchart for describing an operation of a base station ina mobile communication system according to a third embodiment of thepresent invention;

FIG. 12 is a sequence diagram for describing an uplink communicationmethod according to a first modified example of the third embodiment;

FIG. 13 is a sequence diagram for describing an uplink communicationmethod according to a second modified example of the third embodiment;

FIG. 14 is a diagram showing a data packet construction according to afourth modified example of the third embodiment;

FIG. 15 is a diagram showing a construction of the user identificationportion (time-division multiplexed) illustrated in FIG. 14;

FIG. 16 is a diagram showing a construction of the user identificationportion (frequency-division multiplexed) illustrated in FIG. 14;

FIG. 17 is a diagram showing a construction of the user identificationportion (code-division multiplexed) illustrated in FIG. 14;

FIG. 18 is a diagram for describing a method for encoding a data portionon a mobile station according to a first mode of a sixth modifiedexample of the third embodiment;

FIG. 19 is a block diagram showing a construction of a base stationcorresponding to the mobile station of FIG. 18;

FIG. 20 is a diagram for describing a method for encoding a data portionon a mobile station according to a second mode of the sixth modifiedexample of the third embodiment;

FIG. 21 is a block diagram showing a construction of a base stationcorresponding the mobile station of FIG. 20;

FIG. 22 is a flowchart for describing an operation of the base stationof FIG. 19;

FIG. 23 is a flowchart for describing an operation of the base stationof FIG. 21;

FIG. 24 is a flowchart for describing an operation of a mobile stationcorresponding to a base station shown in FIG. 19 or FIG. 21; and

FIG. 25 is a sequence diagram for describing conventional procedures foruplink packet transmission.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) (A) First Embodiment

FIG. 1 is a block diagram showing a construction of a radio mobilestation, which is a constituent of a mobile communication systemaccording to a first embodiment of the present invention; FIG. 2 is ablock diagram showing a construction of a radio base station, which is aconstituent of the same system. The radio mobile station (hereinafterwill be simply called the “mobile station”) 1 in FIG. 1 accesses theradio base station (hereinafter will be simply called the “basestation”) 2 in FIG. 2 by radio for establishing communicationtherebetween. Here, downlink communication, from the base-station 2 tothe mobile station 1, is performed, for example, based on the HSDPAscheme, and uplink communication, from the mobile station 1 to the basestation 2, is performed, for example, based on the HSUPA scheme. Theabove mobile communication system includes one or more mobile stations 1of FIG. 1 and one or more base stations 2 of FIG. 2.

As shown in FIG. 1, with attention focused on its important part, themobile station 1 includes: a data queue 10; an ACK/NACK/DTX evaluatingunit 11; a retransmission buffer 12; a timer 13; a transmitter 14; areceiver 15; a demodulator unit 16; and a scheduling informationtransmitter unit 17. As shown in FIG. 2, with attention focused on itsimportant part, the base station 2 includes: a receiver 20; a CRC andACK/NACK evaluating unit 21; an SI separating unit 22; a scheduler 23; atransmitter 24.

Here, in the mobile station 1 of FIG. 1, the data queue 10 holds datapackets (uplink signals) waiting for transmission; the ACK/NACK/DTXevaluating unit (hereinafter will be also simply called the “evaluatingunit”) 11 evaluates if ACK or NACK has been received from the basestation 2 as a result of data demodulation by the demodulator unit 16,or if no data packet (downlink signal) is received from the base station2 (DTX). Upon confirmation of receipt of ACK, the evaluating unit 11takes out a data packet waiting for transmission from the data queue 10and sends the data packet to the transmitter 14. Upon confirmation ofreceipt of NACK, the evaluating unit 11 takes out an object data packet,which has already been transmitted, from the retransmission buffer 12,and then sends the object data packet to the transmitter 14.

The timer 13 measures a predetermined time period elapsed after the datapacket is transferred to the transmitter 14, that is, after the datapacket is sent to the base station 2. If the evaluating unit 11 does notconfirm the receipt of ACK or NACK even after elapse of thepredetermined time, the timer 13 gives the evaluating unit 11 a triggerwhich makes the evaluating unit 11 end a standby mode for receiving ACKor NACK and makes the transmission processing proceed to the next step.

The transmitter 14, which transmits uplink transmission data packetsfrom the evaluating unit 11 to the base station 2 by radio, hasnecessary radio transmission processing functions such as modulation andspread of transmission data packets, and upconversion of the datapackets to radio frequencies.

The receiver 15, which receives data packets sent from the base station2 by radio at radio frequencies, has necessary radio receptionprocessing functions such as downconversion of the data packets to anintermediate frequency (IF) band and a baseband. The demodulator unit 16performs necessary demodulation processing to the baseband signal fromthe receiver 15, the modulation processing corresponding to thetransmission modulation scheme {e.g., QPSK (Quadrature Phase ShiftKeying) or 16-QAM (Quadrature Amplitude Modulation)} used on the basestation 2.

The scheduling information transmitter unit 17 transmits schedulinginformation (SI) (a transmission request for obtaining transmissionpermission from the base station 2), such as a transmission rateassignment request to the base station 2, to the base station 2 via thetransmitter 14. In the present example, as shown in FIG. 4, thescheduling information transmitter unit 17 generates a signal (datapacket) in which uplink data (transmission user data) to the basestation 2 is added to the scheduling information, and then transmits thegenerated data to the base station 2. In other words, the transmitter 14functions as a transmitter means for transmitting a transmission requestto the base station 2 in order to obtain transmission permission fromthe base station 2; the scheduling information transmitter unit 17functions as a data adding means for adding uplink data to the abovetransmission request.

On the other hand, in the base station 2 of FIG. 2, the receiver 20,which receives data packets sent from the mobile station 1 at radiofrequencies, has necessary radio reception processing functions such asdownconversion of the data packet to an intermediate frequency (IF) bandor a baseband and demodulation processing by QPSK or 16-QAM of the datapacket. The CRC and ACK/NACK evaluating unit 21 performs CRC on abaseband signal received from the receiver 20 to carry out ACK/NACKevaluation. More precisely, if the CRC reveals a normal result, the CRCand ACK/NACK evaluating unit 21 generates ACK; if the CRC reveals anabnormal result, the CRC and ACK/NACK evaluating unit 21 generates NACK.

The SI separating unit 22 separates and extracts the schedulinginformation from the received baseband signal, and the scheduler 23performs sending-out scheduling of downlink (destined to the mobilestation 1) data packet. The scheduling is determined based on suchinformation as the quality of a received data packet, the amount ofbuffer remaining, and priority.

The transmitter 24, which transmits downlink transmission data packetsby radio, has radio transmission processing functions such as modulationand spread of transmission data packets and upconversion of the datapackets to radio frequencies.

Now, referring to FIG. 3, a description will made hereinbelow of anoperation of a mobile communication system of the present embodimentwith the above-described construction.

At execution of HSUPA, the mobile station (UE) 1 transmits a randomaccess signal, including a signature (information identifying eachmobile station 1), to the base station (BTS) 2 at initiation of datatransmission. The random access signal is sent through a common channelas an uplink data packet (step S1). When receiving the random accesssignal, the base station 2 transmits a reply to the access signal to themobile station 1 (step 2), whereby a communication path is establishedover the common channel between the mobile station 1 and the basestation 2.

Upon receipt of the above reply, the mobile station 1 generates a signal(data packet) in which scheduling information (transmission rateassignment request) is added to the uplink transmission user data, asalready described referring to FIG. 4, in order to request the basestation 2 to establish a dedicated channel, and then transmits thegenerated signal to the base station 2 through the communication pathestablished over the foregoing common channel (step S3). Upon receipt ofthe above transmission rate assignment request, the base station 2evaluates whether or not the requested rate can be assigned to themobile station 1. If the assignment is available, a message to thateffect is sent back to the mobile station 1 as a transmission rateassignment reply (step S4).

When the mobile station 1 receives the transmission rate assignmentreply from the base station 2, a dedicated channel is establishedbetween the mobile station 1 and the base station 2, whereby the mobilestation 1 is ready for transmitting an uplink data packet. The mobilestation 1 then starts to send an uplink data packet at the assigned ratethrough the assigned dedicated channel (step S5). If the base station 2decides that it is impossible to assign the requested rate, it ispossible for the base station 2, for example, to assign the maximum ratewhich can be assigned to the mobile station 1 at that time.

As described so far, according to the system of the present example,since an uplink data packet is added (superimposed) to a transmissionrate request sent from the mobile station 1 to the base station 2, it ispossible to reduce the procedures in need for starting datatransmission, in comparison with the prior art. This also makes itpossible to shorten a call-setting time, thereby reducing delay untilthe start of data transmission. In this case, the amount of data to beadded depends on the transmission rate of the dedicated channel, so thatthe transmission rate is kept lower than that of normal uplink packettransmission. However, since the time until the start of datatransmission is shortened, throughput is expected to be improved.

(B) Second Embodiment

FIG. 5 is a block diagram showing a construction of a radio mobilestation, which is a constituent of a mobile communication systemaccording to a second embodiment of the present invention; FIG. 6 is ablock diagram showing a construction of a radio base station, which is aconstituent of the same system. The mobile station 1 of FIG. 5 is alsocapable of accessing the base station 2 of FIG. 6 by radio forestablishing communication therebetween. In this case, also, downlinkcommunication, from the base station 2 to the mobile station 1, isperformed, for example, based on the HSDPA scheme, and uplinkcommunication, from the mobile station 1 to the base station 2, isperformed, for example, based on the HSUPA scheme.

The mobile station 1 of FIG. 5 differs from the mobile station 1 of FIG.1 in that a signature generating unit 18 is added thereto. The basestation 2 of FIG. 6 differs from the base station 2 of FIG. 2 in that asignature separating unit 25 is added thereto.

Here, the signature generating unit 18 of the mobile station 1 generatesa signature (information identifying each mobile station 1) as physicallayer information contained in a random access signal (a channelestablishment request to the base station 2 for establishing andedicated channel for transmitting scheduling information, which is atransmission request, therethrough) to be transmitted to the basestation 2 through a common channel at the start of data transmission. Inthe present example, as shown in FIG. 8, for example, a signal (datapacket) in which uplink user data is added to the generated signature istransmitted by the transmitter 14.

In other words, the signature generating unit 18 and the transmitter 14serve as a transmitter means for transmitting the above channelestablishment request and also as an uplink data adding means for addinguplink data to the channel establishment request. Here, the signaturegenerating unit 18 is not used (does not operate) in uplink datatransmission other than a random access signal.

The signature separating unit 25 of the base station 2 separates andextracts the above signature from the data packet received by thereceiver 20. From this signature, a mobile station 1 which hastransmitted the received data packet is identified, and the transmitter24 sends back a reply to the random access signal to the identifiedmobile station 1.

Now, referring to FIG. 7, a description will be made hereinbelow of anoperation of a mobile communication system of the present embodimentwith the above-described construction. At execution of HSUPA, the mobilestation (UE) 1 generates a signal (see FIG. 8) in which uplink data(user data) is added to a random access signal including a signature atthe start of data transmission, and then sends the generated signal tothe base station (BTS) 2 through a common channel (step S11). Uponreceipt of this signal on the base station 2, the signature separatingunit 25 separates and extracts the signature, based on which a mobilestation 1 which has transmitted the above random access signal isidentified, and a reply to the random access signal is transmitted tothe identified mobile station 1 (step S12). As a result, a communicationpath is established over a common channel between the mobile station 1and the base station 2.

After that, as in the case of FIG. 3, upon receipt of the above reply,the mobile station 1 generates a signal (data packet) in whichscheduling information (transmission rate assignment request) is addedto the uplink transmission user data in order to request the basestation 2 to establish (set) a dedicated channel, and then transmits thegenerated signal to the base station 2 through the common channel (stepS13). The base station 2 sends back a transmission rate assignment replyto the mobile station 1 (step S14), and the mobile station 1 sends anuplink data packet at the rate assigned by the transmission rateassignment reply (step S15).

In this example, as described above, uplink data (user data) is addedalso to a random access signal sent from the mobile station 1 to thebase station 2, so that it is possible to further reduce delay until theinitial transmission in comparison with the first embodiment. Here, achannel used in random access is normally a common channel, whosetransmission rate is lower than that of dedicated channels, so that theamount of user data to be added is limited. However, since the delayuntil the initial transmission is more reduced in comparison with thefirst embodiment, further improvement in throughput is expected.

Here, although uplink data is added to both the random access signal andthe transmission rate request (scheduling information) in the presentexample, uplink data may be added only to the random access signal. Inthis case, the time until the start of uplink data transmission canstill be reduced in comparison with the prior art, so that improvementin throughput is expected.

(B1) Modified Example of Second Embodiment

In the foregoing second embodiment, it is possible for the base station2 to notify the mobile station 1 of ACK/NACK with respect to uplinkpacket transmission from the mobile station 1 together withpermission/non-permission for the following uplink transmission(transmission rate assignment permission/non-permission). Moreprecisely, as shown in FIG. 10, the transmitter 24 is capable ofgenerating a signal (data packet) in which transmission ratepermission/non-permission information is added to ACK/NACK informationto be transmitted to the mobile station 1 (step S14′ of FIG. 9).

In other words, the transmitter 24 functions as a reply informationtransmitter means for transmitting reply information (ACK/NACK), whichindicates whether or not an uplink data packet has been normallyreceived from the mobile station 1, to the mobile station 1. Thescheduler 23 functions as a notification information adding means foradding transmission permission/non-permission information, in responseto a transmission request from the mobile station 1, to the replyinformation. Note that the other procedures in FIG. 9 are the same as orsimilar to those of FIG. 7.

This arrangement will simplify the procedures of downlink transmission.More precisely, ACK/NACK and uplink transmission rate assignmentpermission/non-permission are conventionally defined to be performed indifferent radio channels. For example, in HSUPA, ACK/NACK is transmittedthrough an E-HICH {E-DCH (Enhanced-Dedicated CHannel) HARQ (HybridAutomatic Repeat reQuest) Acknowledgement Indicator Channel}; assignmentpermission/non-permission is transmitted through an E-AGCH (E-DCHAbsolute Grant Channel) or an E-RGCH (E-DCH Relative Grant Channel). Incontrast, in the present example, ACK/NACK and transmission ratepermission/non-permission can be notified to the mobile station 1through the same channel at the same time. Accordingly, the time untilthe start of data transmission is reduced, thereby improving throughput.

(C) Third Embodiment

In the above embodiments, the base station 2 monitors (measures) anuplink communication state based on the amount of uplink traffic and theamount of interference. If the traffic amount or the interference amountis below a specific amount (reference value), each mobile station 1 isnotified to that effect, thereby making it possible for each mobilestation 1 to perform uplink transmission without prior permission of thebase station 2.

That is, as shown in FIG. 11, the base station 2 monitors an uplinkcommunication state based on the traffic amount and the interferenceamount (step S21), and evaluates whether or not the traffic amount andthe interference amount are not greater than a specific amount(reference value) (step S22). If those amounts are not greater than thereference value, the base station 2 judges that the uplink communicationstate is good, and notifies each mobile station 1 that prior permissionis not necessary before starting of data transmission (from Yes route ofstep S22 to step S23). If those amounts are greater than the referencevalue, the base station 2 judges that the uplink communication state isnot good, and then notifies each mobile station 1 that prior permissionis necessary before starting of data transmission (from No route of stepS22 to step S24).

In other words, the base station 2 selectively switches between a mode(first mode) in which uplink data transmission can be performed withoutprior permission and another mode (second mode) in which uplink datatransmission can be performed only after prior permission given. Such afunction is given to the above-described scheduler 23. In this case, thescheduler 23 has the following functions:

(1) a function as a communication state monitoring means 231 whichmonitors an uplink communication state between the base station 2 andthe mobile station 1 by executing the above step S21;

(2) a function as an evaluating means 232 which evaluates whether or notthe quality of an uplink communication state is a specific level orhigher by executing the above step S22;

(3) a function as a mode selecting means 233 which selectively executesthe above steps S23 and S24, thereby selecting the foregoing first modeas an operation mode if the evaluating means 232 judges that the qualityof the uplink communication state is not lower than a specific level,and selecting the foregoing second mode as an operation mode if theevaluating means 232 judges that the quality of the uplink communicationstate is lower than a specific level.

With this arrangement, under a condition where the uplink communicationstate is good, the procedures which were necessary in uplink datatransmission are eliminated, so that delay until data transmission isalso eliminated, thereby improving throughput.

(C1) First Modified Example of Third Embodiment

Assuming that each mobile station 1 receives a notification of a mode inwhich the mobile station 1 can start data transmission without obtainingprior permission from the base station 2, and that the mobile station 1starts uplink packet transmission without permission of the base station2, there is a possibility that a collision happens between the uplinktransmission (data packets) from more than one mobile station 1. In sucha case, the collided data packets are discarded on the base station 2.At this time, the mobile station 1 normally performs retransmissionafter waiting a random period. This makes it possible to lower thepossibility of a collision at the time of retransmission performed, butthere is another possibility that delay until the retransmission isenlarged.

Therefore, in the present example, if mobile stations 1 that havesimultaneously transmitted the collided packets can be identified, thebase station 2 requests the mobile stations 1 to retransmit the packets.More precisely, as shown in FIG. 12, it is assumed that the mobilestations 1-1 and 1-2 simultaneously transmit uplink data (step S31), andthat a collision occurs on the base station 2. Here, note that each ofthe mobile stations 1-1 and 1-2 performs uplink data transmission usinga frame format including a signature, as already described withreference to FIG. 8.

If the mobile stations 1-1 and 1-2 which have transmitted the collideddata packets are identifiable from the above signature, the base station2 sends a retransmission request to the mobile stations 1-1 and 1-2 atdifferent timings (steps S32 and S33). This makes the mobile stations1-1 and 1-2 transmit uplink data at different timings (steps S34 andS35).

The foregoing operation is realized on the base station 2 by thescheduler 23 which functions as an uplink data collision monitoringmeans and the transmitter 24 which functions as a retransmission timingnotifying means. The scheduler 23, as an uplink data collisionmonitoring means, monitors whether or not a collision occurs betweenuplink data transmission from two or more mobile stations 1 while thebase station 2 is operating in the foregoing first mode. If a collisionis detected by the uplink data collision monitoring means, thetransmitter 24, as a retransmission timing notifying means, notifies themobile stations that have transmitted the collided uplink data oftimings for retransmitting the uplink data.

With this arrangement, it is possible to minimize delay in uplink datatransmission and to reliably avoid a collision when the uplink data isretransmitted.

(C2) Second Modified Example of Third Embodiment

While the base station 2 is waiting for data retransmission from themobile stations 1-1 and 1-2, it is preferable that the base station 2broadcast a busy signal to prevent other mobile stations fromtransmitting data. More specifically, as shown in FIG. 13, when the basestation 2 sends retransmission requests to the mobile stations 1-1 and1-2 due to a collision which has occurred between the uplinktransmission data packets of the mobile stations 1-1 and 1-2 (steps S32and S33), the base station 2 broadcasts a busy signal through, forexample, a common channel until retransmission from the mobile stations1-1 and 1-2 (steps S34 and S35) is performed (or during a period inwhich retransmission is expected) (step S36).

In other words, the base station 2 functions as a busy state informingmeans which informs each mobile station 1 within its cell of a busystate during a time period in which uplink data retransmission isexpected from the relevant mobile stations based on a notification ofretransmission timing sent by the transmitter 24 as the retransmissiontiming notifying means. This function may be also given to the scheduler23.

While receiving the busy signal, another mobile station 1-3 refrainsfrom uplink data transmission. After transmission of the busy signalfrom the base station 2 is ended, so that the busy signal is no longerreceived, the mobile station 1-3 starts uplink data transmission (stepS37). This arrangement makes it possible to further lower thepossibility of a collision of uplink transmission data packets.

(C3) Third Modified Example of Third Embodiment

Here, the length of data packets transmitted from the mobile stations1-1, 1-2, and 1-3 (hereinafter will be called the “mobile station 1”when no distinction is made there among) and the base station 2 arepreferably fixed. This makes it easy for the mobile station 1 torecognize with which timing retransmission should be performed when acollision of uplink data transmission happens on the base station 2.

(C4) Fourth Modified Example of Third Embodiment

As shown in FIG. 14, a data packet transmitted from the mobile station 1has a user identification portion 5 identifying each user and a dataportion 6 which is a message body. That is, the mobile station 1 has afunction of an uplink data generating means which generates an uplinkdata packet having a user identification portion 5 identifying eachmobile station 1 and a data portion 6 which is a message body, and alsoa function of an uplink data transmitter means which transmits theuplink data generated by the uplink data generating means to the basestation 2. These functions are realized as one of the functions of thetransmitter 14. In this case, the mobile station 1 is capable ofperforming stronger error correction processing to the useridentification portion 5 than to the data portion 6.

With this arrangement, even if uplink data packets sent from differentmobile stations 1 collide on the base station 2, it is highly likelythat the base station 2 is capable of decoding at least information ofthe user identification portion 5. Thus, if decoding of information ofthe data portion 6 is unavailable, it is possible to identify whichmobile stations 1 have sent the data packets that have collided.

(C5) Fifth Modified Example of Third Embodiment

Further, the user identification portion 5 can be separated into smalldivisions in the time axis direction, thereby being time-divisionmultiplexed (TDM), as shown in FIG. 15, or it can be separated in thefrequency direction, thereby being orthogonal frequency-divisionmultiplexed (OFDM), as shown in FIG. 16, or it can be code-divisionmultiplexed (CDM). This makes it highly likely that even if a collisionof uplink data packets transmitted from different mobile stations 1occurs, the base station 2 is capable of decoding at least informationof the user identification portion 5. As a result, it is possible toevaluate which mobile stations 1 have transmitted the uplink datapackets that collided.

(C6) Sixth Modified Example of Third Embodiment

Next, on the assumption that when data packets transmitted fromdifferent mobile stations 1 collides, the base station 2 can identifythe mobile stations 1 (users) based on information of the useridentification portions 5, and that information of one of the dataportions 6 is normally decoded, a description will be made hereinbelowof a method which makes it possible to evaluate which user (mobilestation 1) the decoded data portion 6 corresponds to.

(C6.1) First Mode of Sixth Modified Example

In this example, as shown in FIG. 18, the mobile station 1 (transmitter14: see FIG. 1 and FIG. 5) encodes {performs multiplication by amultiplier (encoding means) 141 or an exclusive OR operation} a messageto be stored in a data portion 6 using information (user identificationinformation) of a user identification portion 5, and the encodedinformation is stored in the data portion 6. The user identificationportion 5 stores a signal obtained by multiplying the above useridentification information and the modulation signal together by meansof a multiplier 142. This method makes it possible to make the useridentification information contained (superposed) in the data portion 6without significantly reducing the data amount in the data portion 6.

Such encoding necessitates the user identification information fordecoding (reproducing) the data portion, and thus the base station 2needs to decode the user identification portion 5 prior to the dataportion 6. In this case, as shown in FIG. 19, the base station 2includes: a data portion separating unit 26 which separates the useridentification portion 5 and the data portion 6 from an output (anuplink data packet received) of the receiver (receiver means) 20; and amultiplier 27 which multiplies information of the user identificationportion 5 and information of the data portion 6, separated by the dataportion separating unit 26, together, to decode (reproduce) informationof the data portion 6 (message body). Here, in FIG. 19, like referencenumbers and characters designate similar parts or elements throughoutseveral views of the embodiments, unless otherwise described.

With this arrangement, the base station 2 decodes the useridentification portion 5 prior to the data portion 6, and using thedecoded information, the base station 2 decodes information of the dataportion 6. Accordingly, at a collision of data packets from differentmobile stations 1, when information of the user identification portions5 is correctly decoded, so that the mobile stations (users) 1 areidentified, and also when information of one of the data portions 6 iscorrectly decoded, it is possible to decide which user (mobile station1) the decoded data portion 6 corresponds to. As a result, it ispossible to identify a mobile station 1 to which the above-mentionedretransmission request and ACK/NACK are to be transmitted.

(C6.2) Second Mode of Sixth Modified Example

In this instance, as shown in FIG. 20, on the mobile station 1(transmitter 14), user identification information, as it is, iscontained (inserted) in a data portion 6 as a part thereof. That is, inthis case, the transmitter 14 functions as an inserting means forinserting information of the user identification portion 5 into the dataportion 6. This makes it possible to easily take out user identificationinformation by decoding the information of the user identificationportion 5 from the data portion 6 on the receiver end (base station 2).Here, as shown in FIG. 21, the base station 2 includes, as well as thedata portion separating unit 26 already described: a user identificationinformation separating unit 28 which separates user identificationinformation from the data portion 6 that has been separated by the dataportion separating unit 26; and a comparing unit 29 which compares useridentification information separated by the user identificationinformation separating unit 28 with user identification informationseparated by the data portion separating unit 26.

With this arrangement, on the base station 2, the data portionseparating unit 26 separates the user identification portion 5 and thedata portion 6 from an output (uplink data packet received) of thereceiver (receiver means) 20, and the user identification informationseparating unit 28 further separates user identification informationcontained in the data portion 6, and the comparing unit 29 compares theuser identification information separated by data portion separatingunit 28 with the user identification information separated by the useridentification information separating unit 26. Based on the comparisonresult (match/mismatch), the base station 2 is capable of deciding fromwhich user (mobile station 1) the data portion 6 has been transmitted.As a result, a mobile station 1 to which the aforementionedretransmission request and ACK/NACK are to be transmitted is identified.

(C7) Seventh Modified Example of Third Embodiment

Concretely, when a user identification portion 5 and its correspondingdata portion 6 are correctly received and decoded, the base station 2transmits ACK to the mobile station 1. On the other hand, when only theuser identification portion 5 is correctly received and decoded, thebase station 2 transmits NACK to the mobile station 1. In addition, incases where the method described in the above section (C6) is employed,and when the base station 2 correctly receives and decodes only a dataportion 6, the base station 2 transmits ACK to the mobile station 1because the user can be identified based on the user identificationinformation contained in the data portion 6.

Here, when the base station 2 transmits ACK or NACK to the mobilestation 1, the next scheduling information can be simultaneously (added)transmitted. FIG. 22 shows an operation of the base station 2 in whichthe method described in the above section (C6.1) is employed; FIG. 23shows an operation of the base station 2 in which the method describedin the above section (C6.2) is employed.

(C7.1) First Mode of Seventh Modified Example

When the mobile station 1 encodes a data portion 6 using useridentification information at transmission of a data packet, asdescribed in the above section (C6.1), the base station 2, as shown inFIG. 22, decodes a user identification portion 5 (step S41), and thendecodes the data portion 6 (step S42). After that, the CRC and ACK/NACKevaluating unit 21 performs CRC (step S43). If the CRC reveals an “OK”result (a correct decoding result has been obtained), the base station 2generates ACK (step S44), and if the check reveals a “NG” result (acorrect decoding result has not been obtained), the base station 2generates NACK (step S45).

Subsequently, on the base station 2, the scheduler 23 evaluates whetheror not scheduling information (permission for the following datatransmission) to be transmitted to the mobile station 1 exists (stepS46). If such scheduling information to be transmitted is present, thescheduling information is transmitted to the mobile station 1 togetherwith the above ACK or NACK (from Yes route of step S46 to step S47), andif the scheduling information to be transmitted is not present, theabove ACK or NACK is transmitted to the mobile station 1 as it is (fromNo route of step S46 to step S48).

That is, if a data packet (user identification portion 5 and dataportion 6) received from the mobile station 1 is correctly decoded, thebase station 2 transmits permission for the following data transmission,together with ACK, to the mobile station 1 that has been identifiedbased on the decoded user identification information. If a useridentification portion 5 is correctly decoded but a data portion 6 isnot correctly decoded, the base station 2 transmits permission for thefollowing data transmission, together with NACK, to the mobile station 1that has been identified based on the decoded user identificationinformation.

In other words, the base station 2 of the present example realizes afunction of a reply and transmission permission transmitter means whichtransmits, if the user identification portion 5 and the data portion 6are correctly decoded by the scheduler 23 and the transmitter 24,permission for the following uplink data transmission, together withreply information ACK indicating normal reception, to a mobile station 1identified by information of the user identification portion 5, andwhich reply and transmission permission transmitter means transmits, ifthe user identification portion 5 is correctly decoded and the dataportion 6 is not correctly decoded, permission for the following uplinkdata transmission, together with reply information NACK indicatingabnormal reception, to a mobile station 1 identified by information ofthe user identification portion 5.

With this arrangement, in comparison with a case in which ACK/NACK andthe scheduling information are separately transmitted to the mobilestation 1, the procedures of uplink data transmission are furthersimplified, so that delay in uplink data transmission is reduced,thereby further improving throughput.

(C7.2) Second Mode of Seventh Embodiment

As described in the above section (C6.2), when the mobile station 1transmits a data packet in which user identification information isinserted in a data portion 6 thereof, the data portion separating unit26 and the user identification information separating unit 28 (see FIG.21) of the base station 2 separate, as shown in FIG. 23, a useridentification portion 5 and a data portion 6 of the received datapacket (step S51), and the user identification information is decoded(step S52), and the CRC and ACK/NACK evaluating unit 21 performs CRC(step S53).

If the CRC result reveals an “OK” result, the i-th user identificationinformation, and user identification information contained in the dataportion 6 are compared by the comparing unit 29, to evaluate if theymatch up (step S54 and step S55). If the two user identificationinformation items match up, the base station 2 (CRC and ACK/NACKevaluating unit 21) generates ACK as a reply to the mobile station 1(from Yes route of step S55 to step S56), and if the two do not matchup, the base station 2 generates NACK (from NO route of step S55 to stepS57).

After that, on the base station 2, the scheduler 23 evaluates whether ornot scheduling information (permission for the following datatransmission) to be transmitted to the mobile station 1 exists (stepS58). If the scheduling information to be transmitted is present, thescheduling information is sent to the mobile station 1 together with theACK or NACK (from Yes route of step S58 to step S58 a). If thescheduling information to be transmitted is not present, the above ACKor NACK is transmitted to the mobile station 1 as it is (from No routeof step S58 to step S58 b).

After that, the base station 2 checks whether or not processing has beencompleted for data packets (the number of packet=N) received from allthe users (mobile stations 1) decoded (i<N?: step S59). If theprocessing has not been completed, the value of i is incremented by 1(i=i+1) (from Yes route of step S59 to step S60), the above processingof step S54 and thereafter is repeated to the (i+1)th useridentification information item and its data portion, until theprocessing has been completed (until a “No” decision is obtained at stepS59).

That is, on the base station 2, the scheduler 23 and the transmitter 24realize a function of a reply and transmission permission transmittermeans, which transmits, if the data portion 6 is correctly decoded,permission for the following data transmission to the mobile station 1identified based on the decoded information (user identificationinformation contained in the data portion 6), together with replyinformation ACK indicating normal reception, and which transmits, if theuser identification portion 5 is correctly decoded but the data portion6 is not correctly decoded, the permission for the following datatransmission to the mobile station 1 identified by information of theuser identification portion 5, together with reply information NACKindicating abnormal reception.

As described so far, in comparison with a case in which ACK/NACK and thescheduling information are separately transmitted to the mobile station1, the procedures of uplink data transmission are further simplified, sothat delay in uplink data transmission is reduced, thereby furtherimproving throughput.

(C8) Eight Modified Example of Third Embodiment

Next, referring to FIG. 24, a description will be made hereinbelow of anoperation of the mobile station 1 when the base station 2 transmitsscheduling information together with ACK or NACK, as described in theabove section (C7). The construction of the mobile station 1 is similarto that of FIG. 1.

As shown in FIG. 24, the mobile station 1 evaluates whether or not atransmission schedule (that is, a data packet to be transmitted) ispresent (step S61). If there is no transmission schedule, the processingends (No route of step S61). On the other hand, if there is atransmission schedule, the following (new) data packet is taken out fromthe data queue 10 (step S62), and the data packet is transmitted fromthe transmitter 14. Here, the time value of the timer 13 is reset to “0”(step S63).

After that, the mobile station 1 evaluates whether or not downlinksignaling (data packet) is received from the base station 2 (step S64).If the evaluation result is negative (No route of step S64), it isfurther evaluated whether of not the timer value of the timer 13 isbelow a specific value T (T is a real number not smaller than 0) (stepS65). If the timer value is below the specific value T (Yes route ofstep S65), the timer value is incremented (step S66 a), and thenmonitoring is kept continued thereafter, while the time value isincremented, until a downlink data packet is received from the basestation 2. Here, if the timer value reaches the specific value T withoutreceiving a downlink data packet from the base station 2, the mobilestation 1 transmits a retransmission request to the base station 2 andresets the timer value of the timer 13 to “0” (from No route of step S65to steps S67 and S63).

On the other hand, if a downlink data packet is received from the basestation 2, the mobile station 1 evaluates whether the data packetreceived is ACK or NACK (step S66 b). If it is NACK, the mobile station1 sends a retransmission request to the base station 2 (step S67). If itis ACK, the mobile station 1 further evaluates whether or not thefollowing data packet is present in the data queue 10 (step S68). If thefollowing data packet exists, the mobile station 1 transmits the datapacket (from Yes route of step S68 to step S62), and if the data packetdoes not exist, the mobile station 1 ends the processing (No route ofstep S68).

That is, in a case where the data packet received from the base station2 is ACK, and also where the following transmission data exists, if themobile station 1 receives schedule information, the mobile station 1transmits the following data with the timing of the schedulinginformation. If the scheduling information is not received, the mobilestation 1 recommences the processing from transmission of aretransmission request. In contrast, if the data packet received formthe base station 2 is NACK, and also if the scheduling information isreceived, the mobile station 1 transmits the following data with thetiming of the scheduling information.

If the mobile station 1 has not received scheduling information, or ifthe mobile station 1 has received nothing (DTX), the mobile station 1recommences the processing from transmission of a retransmissionrequest.

In other words, the receiver 15 of the mobile station 1 has a functionof a reply and transmission permission receiver means which receivesscheduling information (permission for uplink data transmission)together with reply information (ACK/NACK) indicating normal receptionor abnormal reception of uplink data from the base station 2. Ifscheduling information is received together with ACK, the transmitter 14of the mobile station 1, as an uplink data transmitter means, transmitsthe following uplink data packet in pursuance of the schedulinginformation. If scheduling information is received together with NACK,the transmitter 14 transmits an uplink data retransmission request tothe base station 2 in pursuance of the scheduling information. Further,if no downlink data packet is received from the base station 2 within aspecific time period (T), the transmitter 14 transmits an uplink dataretransmission request to the base station 2.

Here, in a case where a data packet received from the base station 2 isNACK, data retransmission is available even if the above schedulinginformation has not been received, under a condition that there is suchan agreement between the mobile station 1 and the base station 2(network).

With this arrangement, in comparison with a case in which ACK/NACK andthe scheduling information are separately transmitted to the mobilestation 1, the procedures of uplink data transmission are simplified, sothat delay in uplink data transmission is reduced, thereby furtherimproving throughput.

Further, the present invention should by no means be limited to theabove-illustrated embodiment, but various changes or modifications maybe suggested without departing from the gist of the invention.

1. A communication method in a mobile communication system including atleast one mobile station and a base station, which performs radiocommunication with the mobile station, said communication methodcomprising: on the mobile station, adding uplink user data to a channelestablishment request sent to the base station for establishing achannel in order to send a transmission request sent to the base stationfor obtaining permission for data transmission therethrough.
 2. Acommunication method as set forth in claim 1, further comprising: on thebase station, adding transmission permission/non-permission notificationinformation, indicating whether or not data transmission is permitted inresponse to the transmission request, to reply information sent to themobile station, which reply information indicates whether or not theuplink data sent from the mobile station has been normally received. 3.A communication method in a mobile communication system including atleast one mobile station and a base station, said method comprising: onthe base station, transmitting, when an user identification portionidentifying each mobile station and a data portion which is a messagebody, which are included in the uplink data transmitted from the mobilestation, are correctly decoded, permission for the following uplink datatransmission, together with reply information indicating a normalreception, to a mobile station identified by information of the useridentification portion; and transmitting, when the user identificationportion is correctly decoded but the data portion is not correctlydecoded, permission for the following uplink data transmission, togetherwith reply information indicating an abnormal reception, to a mobilestation identified by information of the user identification portion. 4.A communication method as set forth in claim 3, further comprising: onthe base station, wherein said base station is operable in a first modein which the base station's permission is not necessary when the mobilestation transmits the uplink data, and a second mode in which the basestation's permission is necessary when the mobile station transmits theuplink data, performing radio communication with the mobile station;monitoring an uplink communication state between the base station andthe mobile station; operating in the first mode if the uplinkcommunication state is of a specific or higher level of quality;operating in the second mode if the uplink communication state is ofquality lower than the specific level; monitoring, while operating inthe first mode, whether or not a collision occurs in uplink datatransmission from two or more mobile stations; and notifying each of themobile station, if a collision occurs, of retransmission timing in theuplink data transmission.
 5. A communication method as set forth inclaim 4, further comprising: on the base station, informing the two ormore mobile stations of a busy state during a specific period in whichuplink data retransmission is expected based on the notification of theretransmission timing.
 6. A communication method as set forth in claim4, further comprising: on the mobile station, performing the uplink datatransmission using uplink data having a fixed data length.
 7. Acommunication method as set forth in claim 3, wherein the useridentification portion is obtained by time-division multiplexing, orfrequency-division multiplexing, or code-division multiplexing the useridentification information of each of the two or more mobile stations.8. A communication method as set forth in claim 3, further comprising:on the mobile station, encoding the data portion based on information ofthe user identification portion.
 9. A communication method as set forthin claim 8, further comprising: on the base station, performing adecoding process from the user identification portion.
 10. Acommunication method as set forth in claim 9, further comprising: on themobile station, transmitting, if the data transmission permission isreceived from the base station together with the reply informationindicating a normal reception, the following uplink data to the basestation in pursuance of the uplink data transmission permission; andtransmitting, if the data transmission permission is received from thebase station together with the reply information indicating an abnormalreception, an uplink data retransmission request to the base station inpursuance of the uplink data transmission permission.
 11. Acommunication method as set forth in claim 10, further comprising: onthe mobile station, transmitting an uplink data retransmission requestto the base station, if downlink data is not received from the basestation within a specific period.
 12. A communication method as setforth in claim 3, further comprising: on the mobile station, insertinginformation of the user identification portion into the data portion.13. A communication method as set forth in claim 12, further comprising:on the base station, performing a decoding process from the dataportion.
 14. A communication method as set forth in claim 13, furthercomprising: on the base station, transmitting, if the data portion iscorrectly decoded, permission for the following uplink datatransmission, together with reply information indicating a normalreception, to a mobile station identified based on the decodedinformation; and transmitting, if the user identification portion iscorrectly decoded but the data portion is not correctly decoded,permission for the following uplink data transmission, together withreply information indicating an abnormal reception, to a mobile stationidentified by information of the user identification portion.
 15. Amobile station for a mobile communication system including at least onemobile station and a base station, which performs radio communicationwith the mobile station, said mobile station comprising: a transmitterwhich transmits a channel establishment request to the base station forestablishing a channel in order to send a transmission request sent tothe base station for obtaining permission for data transmissiontherethrough; and a data adding unit which adds uplink user data to thechannel establishment request.
 16. A base station for a mobilecommunication system including at least one mobile station and a basestation, which performs radio communication with the mobile station,said base station comprising: a reply information transmitter whichtransmits reply information, indicating whether or not the uplink userdata, which is attached to a channel establishment request forestablishing a channel, sent from the mobile station has been normallyreceived, to the mobile station; and a notification information addingunit which adds transmission permission/non-permission notificationinformation, indicating whether or not data transmission is permitted inresponse to the transmission request, to the reply information to besent to the mobile station.
 17. A base station for a mobilecommunication system including at least one mobile station and a basestation, said base station comprising: a receiving unit which receivesuplink data including a user identification portion identifying eachmobile station and a data portion, which is a message body; a reply andtransmission permission transmitter which transmits, when the useridentification portion is correctly decoded but the data portion is notcorrectly decoded, permission for the following uplink datatransmission, together with reply information indicating an abnormalreception, to a mobile station identified by information of the useridentification portion.
 18. A base station for a mobile communicationsystem as set forth in claim 17, wherein said base station performsradio communication with the mobile station, wherein said mobile stationis operable in a first mode in which the base station's permission isnot necessary when the mobile station transmits uplink data, and asecond mode in which the base station's permission is necessary when themobile station transmits uplink data, said base station furthercomprising: an uplink communication state monitoring unit which monitorsan uplink communication state between the base station and the mobilestation; an evaluating unit which evaluates whether or not thecommunication state monitored by said uplink communication statemonitoring unit is of a specific or higher level of quality; a modeselecting unit which selects the first mode as an operation mode if theevaluation result is positive, and which selects the second mode as anoperation mode if the evaluation result is negative; a data collisionmonitoring unit which monitors, while operating in the first mode,whether or not a collision occurs in uplink data transmission from twoor more mobile stations; and a retransmission timing notifying unitwhich notifies each of the mobile stations, if an occurrence of acollision is detected by said data collision monitoring unit, ofretransmission timing in the uplink data transmission.
 19. A basestation for a mobile communication system as set forth in claim 18,further comprising: a busy state informing unit which informs the two ormore mobile stations of a busy state during a specific period in whichuplink data retransmission is expected based on the notification of theretransmission timing made by said retransmission timing notifying unit.20. A base station for a mobile communication system as set forth inclaim 18, wherein said uplink data is sent out from the mobile stationafter being encoded using information of the user identificationportion; and wherein said base station further has decoding unit whichdecodes the uplink data, received by said receiving unit, from the useridentification portion.
 21. A base station for a mobile communicationsystem as set forth in claim 20, wherein said reply and transmissionpermission transmitter transmits, if the user identification portion andthe data portion are correctly decoded, permission for the followinguplink data transmission, together with reply information indicatingnormal reception, to a mobile station identified by information of theuser identification portion.
 22. A base station for a mobilecommunication system as set forth in claim 21, wherein said reply andtransmission permission transmitter transmits, if the useridentification portion is correctly decoded but the data portion is notcorrectly decoded, permission for the following uplink datatransmission, together with reply information indicating abnormalreception, to a mobile station identified by information of the useridentification portion.
 23. A base station for a mobile communicationsystem as set forth in claim 18, wherein said uplink data is sent outfrom the mobile station after information of the user identificationportion is inserted in the data portion thereof; and wherein said basestation further has decoding unit which decodes the uplink data,received by said receiving unit, from the data portion.
 24. A basestation for a mobile communication system as set forth in claim 23,wherein said reply and transmission permission transmitter transmits, ifthe data portion is correctly decoded, permission for the followinguplink data transmission, together with reply information indicating anormal reception, to a mobile station identified based on the decodedinformation.
 25. A base station for a mobile communication system as setforth in claim 24, wherein said reply and transmission permissiontransmitter transmits, if the user identification portion is correctlydecoded but the data portion is not correctly decoded, permission forthe following uplink data transmission, together with reply informationindicating an abnormal reception, to a mobile station identified byinformation of the user identification portion.
 26. A mobile station fora mobile communication system including at least one mobile station anda base station, which performs radio communication with the mobilestation, in which mobile communication system said base stationnotifies, if a collision occurs in uplink data transmission from two ormore mobile stations, each of the mobile stations of retransmissiontiming in the uplink data transmission, said mobile station comprising:an uplink data generating unit which generates a transmission request ora channel establishment request including: a user identification portionidentifying each mobile station; and a data portion, which is a messagebody; and an uplink data transmitter which transmits the transmissionrequest or the channel establishment request generated by said uplinkdata generating unit to the base station, wherein the mobile stationperforms stronger error correction processing to the user identificationportion than to the data portion.
 27. A mobile station for a mobilecommunication system as set forth in claim 26, wherein said uplink datagenerating unit generates the transmission request or the channelestablishment request as data having a fixed data length.
 28. A mobilestation for a mobile communication system as set forth in claim 26,wherein said uplink data generating unit includes an encoding unit whichencodes the data portion based on information of the user identificationportion.
 29. A mobile station for a mobile communication system as setforth in claim 26, wherein said uplink data generating unit includes aninserting unit which inserts information of the user identificationportion into the data portion.
 30. A mobile station for a mobilecommunication system as set forth in claim 26, said mobile stationfurther comprising: a reply and transmission permission receiver whichreceives permission for transmission request or channel establishmentrequest transmission together with reply information indicating normalor abnormal reception of the transmission request or the channelestablishment request from the base station, wherein said uplinktransmitter transmits, if said reply and transmission permissionreceiver receives the data transmission permission together with thereply information indicating a normal reception, the following uplinkdata to the base station in pursuance of the transmission request or thechannel establishment request transmission permission, and wherein saiduplink data transmitter transmits, if said reply and transmissionpermission receiver receives the data transmission permission togetherwith the reply information indicating an abnormal reception, an uplinkdata retransmission request to the base station in pursuance of theuplink data transmission permission.
 31. A mobile station for a mobilecommunication system as set forth in claim 30, wherein said uplink datatransmitter transmits an uplink data retransmission request to the basestation, if downlink data is not received from the base station within aspecific period.